Where do I find an 8" long 1/2-20 bolt that doesn't suck?

My 9" saga continues. So, I'm setting up my Yukon 3.25" throughbolt cased rearend again, with the new diff, and I get the backlash spot on so I go to torque up the bolts. Set torque wrench to 85ft-lb, walk the bolts up slowly... and they just don't seem to be getting tight. Set to 60, we're there.

Set to 65, we're there.

Set to 70, we're not there. Sloooowly torque each bolt... slooowly... and the first one I'm on starts getting easier.

Commence all the cursing.

This is the third set of bolts I have tried in this housing. They stretch and fail long before I get up to torque. I have seen 85lb everywhere except for one forum where 75 was suggested. I'm not getting even up to 75 before they stretch.

These are Grade 8 bolts, and I am using double height nuts (the studs that came with the housing failed when the supplied nuts stripped) and good hardened washers. Have tried the yellow/gold coated ones from McMaster and I think these latest ones came from Fastenal, but it's been a long time.

I'm tempted to just get another set of the yellow bolts (they're only like $8 each) and only torque them up to 60ft-lb. The rearend in the car now has 10mm bolts torqued to 35 and I'm not blowing the caps out.

So, two things:

What are the bolts coated with? A oiled bolt or hole will result in the same torque being much more preload as your K factor decreases.

Also, it seems the basic generic torque spec for a dry plated coarse 1/2 bolt is 80 lb ft. Now they should not yield at 80, but where did you find 85?

https://www.boltdepot.com/fastener-information/bolts/US-Recommended-Torque.aspx

Also, make sure you're getting bolts with rolled threads instead of cut threads. Some seemingly high class companies ::cough cough:: still accept cut threads, which is like saying occasionally it's OK if my wife is a parrot.

Allegedly the McMaster bolts are rolled.

Forgot to add, there is a shorter bolt that nestles under the pinion support that doesn't feel happy either, but so far it hasn't stretched. I can run a nut all the way down the threaded portion with no issue. It's only the 8" long ones that are failing. And the threads aren't failing, the bolt is stretching.

ARP doesn't list anything over 6", and my attempts to contact Yukon have always been met with silence.

Bolts are lubricated with light oil, not moly or anything ridiculous like that.

I was going to suggest ARP, but they only go up to 6" long.

However, that doesn't mean they may not have a solution if you reached out to them directly.

Also, would GM have factory hardware available at the dealer?

I am pretty sure that 90 lb ft is your bogie for a lubricated fine pitched grade 8:

https://www.fastenal.com/content/feds/pdf/Torque-Tension%20Chart%20for%20A307%20Gr5%20Gr8%20Gr9.pdf

But you indicate getting to yield before then.

Then again, one of the chief engineers here, who has more material science degrees than I can count, is a huge advocate of yielding bolts upon assembly. While the clamping load is not completely peaked, it is about the same at yield as it is at 75% yield or whatever the exact clamping load the torque chart is built around. You can't reuse the bolt, but it will hold just as well as long as you don't neck it down appreciably.

The K factor used for 90 lb ft is 0.15, and you might have a little slicker than that in two well oiled components like that, but you should not be yielding them there regardless. Inspect the bolts you buy next carefully. Counterfeits are everywhere.

What are the nuts coated with? We list torque spec with lube at 78 lb-ft, dry zinc at 130. Maybe try installing them dry?

We stock that size from Lake Erie that are high quality but you probably don't want to wait until the next time you are down here.

Does anyone manufacturer bolts this small with cut threads? All I have seen are rolled.

So this?

https://www.fastenal.com/products/details/18229?r=~|categoryl1:%22600000%20Fasteners%22|~%20~|categoryl2:%22600001%20Bolts%22|~%20~|categoryl3:%22600003%20Cap%20Screws%209and%20Hex%20Bolts%22|~%20~|sattr01:^%22Imperial%20(Inch)%22$|~%20~|sattr03:^%22Hex%20Bolt%22$|~%20~|sattr04:^1/2%22-20$|~%20~|sattr03:^%22Hex%20Cap%20Screw%22$|~%20~|sattr05:^8%22$|~%20~|sattr06:^8$|~

Don't get yellow ones for this application. While it's not likely your problem, the plating can cause issues.

tuna55 wrote: I am pretty sure that 90 lb ft is your bogie for a lubricated fine pitched grade 8: https://www.fastenal.com/content/feds/pdf/Torque-Tension%20Chart%20for%20A307%20Gr5%20Gr8%20Gr9.pdf But you indicate getting to yield before then. Then again, one of the chief engineers here, who has more material science degrees than I can count, is a huge advocate of yielding bolts upon assembly. While the clamping load is not completely peaked, it is about the same at yield as it is at 75% yield or whatever the exact clamping load the torque chart is built around. You can't reuse the bolt, but it will hold just as well as long as you don't neck it down appreciably. The K factor used for 90 lb ft is 0.15, and you might have a little slicker than that in two well oiled components like that, but you should not be yielding them there regardless. Inspect the bolts you buy next carefully. Counterfeits are everywhere.

Hit this on the head. I was digging up the same chart when I saw this posted here. No way you should be anywhere even close to yielding at 80ft-lb. Something funny is going on here...

Knurled wrote: This is the third set of bolts I have tried in this housing. They stretch and fail long before I get up to torque.

You don't have a fastener problem. You have an assembly or tool problem.

When was the last time you had your torque wrench calibrated?

Where are the bolts breaking?

Is fine thread necessary? I just looked up what we have. We can get you some really really good 1/2 x13 studs, but they are in the neighborhood of $100 each. Not super practical.

gearheadmb wrote: Is fine thread necessary? I just looked up what we have. We can get you some really really good 1/2 x13 studs, but they are in the neighborhood of $100 each. Not super practical.

I just rechecked, it looks our prices vary dramatically based on how many we order, so the sale price can be any where from $20 to $100 each. If a coarse thread stud would work let me know thread lengths you want and a quantity and i will get you a quote.

Find a new torque wrench. Do it now.

ya gots your FtLb and NM mixed up?

na, that would make it less, not more.

hmmm, this is strange... Pics of setup?

If it is possibly the wrench ..Find a Snap on tool truck he will have a torque testing Bench set up and or check it against his new tool.

Buy all thread in the spec you want. Weld a nut of the same spec on one end. Cut to length.

Way cheaper than buying a quality bolt.

Spend the savings on wrench calibration ;)

Cheap calibration for clicker torque wrench:

Set torque wrench to desired setting.

Mount piece of pipe to workbench.

Install 12 point 1/2" socket on torque wrench and slide inside pipe.

Get 1/2" drive beam type torque wrench and insert into click wrench socket.

Compare reading on beam when click happens to click set point.

Beam torque wrenches are more accurate, reliable, and better at holding calibration, but they are harder to read precisely and less convenient. In the 3 years I ran the torque wrench calibration program for a nuclear submarine I never once had a beam out of cal, but I had to adjust the clickers almost every time I tested one.

Four different torque wrenches, guys My Precision 1/2", my MAC 3/8", a MAC 1/2", and most recently the I forgot what brand I bought recently to throw into my trailer. We regularly test our torque wrenches on a load cell, as well, since we have one and if you have a tool you might as well get your money's worth out of it. Plus, if you've been wrenching long enough, you know what a certain amount of torque feels like, and it never felt "off". Other than the bolts stretching.

I definitely agree, something funny is going on. I'll post pics when I get home. Actually I'll probably finally start a build thread, it's been long enough.

Ignore the scuzz on the threads, that's dried silicone from the head end after driving the bolts back out of the case. Silicone needs to be there to prevent an oil leak:

Ironically, I specifically got a throughbolt case because I figured it would be stronger.

Could you find head studs in the diameter and length you need? If "yes", then you could nut both ends. Maybe ARP has studs that long?

That is what Da Boss suggested, although my tentative, rapid search of ARP's catalog proved fruitless. Head studs aren't listed by length, just application.

I'm thinkin', just get another set of yellow bolts, torque to 60, call it a day. The M10x1.25 bolts in the Mazda case haven't blown out after all. I found that those yield at about 40 ft-lb, when I mistakenly tried to torque them to 60 one time. Ooops. Stretched the first one like taffy

You can go a little stronger than grade 8 with a socket head cap screw, like McMaster 91251A038.

BrokenYugo wrote: You can go a little stronger than grade 8 with a socket head cap screw, like McMaster 91251A038.

I thought about suggesting that, but there must be a disclaimer.

Don't use SHCS outside! They are for internal use only! I guess "only" if they adhere to standards. They are harder than the grade 8, and therefore more likely to corrode to failure. They will be totally safe inside an oiled rear end, so that could work. people use them outside, but it's a bad call, and once you see an improperly designed 1 1/2" bolt shear off because someone leaned on it the wrong way, you'll respect it!

Have you tried rural king? Not terribly far from your garage space. They have an entire row of bolts, i tend to stock my bolt bin there and their grade 8 seems good in the applications i've put them in.

In reply to tuna55:

TIL, (you got any further reading on that handy?) might not be a good idea then. I think the application here is through bolting the carrier bearing caps to the center section, so one end would be outside.